1. Technical Field
The present invention relates to a locking device that switches locking/unlocking of a rotary shaft.
2. Related Art
In recording apparatuses represented by facsimiles, printers, etc., as a control method for eliminating the skew of a sheet, there is a biting and ejecting type skew removal control as shown in JP-A-2007-84224.
This skew removal control utilizes a downstream roller and an upstream roller, and makes the leading edge of a sheet bitten into the downstream roller and fed toward the downstream by a predetermined amount, and thereafter, reverses the downstream roller in a state where the upstream driving roller has been stopped, and ejects the leading edge of the sheet toward the upstream of the downstream roller. Thereby, the sheet is bent between the upstream roller and the downstream roller, but the leading edge of the sheet follows the downstream roller by virtue of its return behavior, and consequently, skew is corrected.
However, in a case where the above skew removal control is performed on a sheet of high rigidness (high stiffness), such as thick paper, the force to rotate the upstream roller becomes large when the leading edge of the sheet is ejected from the downstream roller. As a result, there is a possibility that the upstream roller may be reversed depending on the case, and thereby, skew may not be eliminated well.
In order to solve such a problem, it is necessary to interpose a clutch that permits only one-way rotation as shown in, for example JP-A-10-331941 between the upstream roller and a motor that drives this roller so that the upstream roller is not reversely rotated and to lock the upstream roller so as not to rotate in a reverse rotation direction.
However, like a recording apparatus that performs records on both sides of a sheet, a roller may be intended to be reversely driven in order to return the sheet to the upstream. Accordingly, in such a case, the clutch that permits only one-way rotation as described above cannot be applied as it is. Accordingly, development of a locking device that can satisfy both rotation driving in normal/reverse directions and reliable prevention (rotational lock) of reverse rotation if necessary has been desired.
Moreover, in a case where a common driving motor is utilized in the upstream roller and the downstream roller, in order to perform the biting and ejecting type skew removal control, the upstream roller should be locked so as not to rotate reversely while the downstream roller is reversely rotated by a predetermined amount, and a locking device that can satisfy such operating conditions is also desired.